In the field of color display devices for images, such as computers and television sets, plasma display devices employing a plasma display panel (PDP) are being increasingly drawing attention due to their advantages of being large, thin and light.
In a PDP, a front board and a rear board are sealed together with a discharge space of predetermined thickness in between. The electrodes and dielectric layer, or partition and phosphor layer, are formed on the front board and rear board respectively by firing structural materials containing organic binder.
During PDP manufacture, impurity gases spread in the PDP by thermal decomposition, typically of the organic binder contained in the glass frit used as sealing material in the sealing process, in particular, that for sealing the front board and rear board. The constituents of these impurity gases are chiefly water vapor, carbon dioxide and hydrocarbon gases. These gases are adsorbed onto the phosphors inside the PDP and cause problems such as degraded discharge characteristic or reduced luminance. This fact is disclosed, for example, in the Japanese Patent Laid-open Application No. 2003-281994 and FPD Technology Outlook, Electronic Journal, Oct. 25, 2000, pp 615-618.
Accordingly, the reduction of impurity gases inside the PDP to stabilize the discharge characteristic and suppress secular change to improve reliability is an important challenge in PDP manufacture.
For this purpose, a commonly used method is to evacuate the PDP while heating it, after sealing the front and rear boards, so as to remove impurity gases inside the PDP, and then inject the discharge gas. FIG. 6 is a sectional view of this type of conventional PDP manufacturing equipment. PDP 60 is configured with front board 61 and rear board 62; and partition 63 and phosphor layer 64 are formed on rear board 62. The surround of front board 61 and rear board 62 is sealed with sealing material 72. Exhaust pipe 65 is connected to rear board 62 of PDP 60, and PDP 60 is placed in furnace 67 equipped with heater 66. The other end of exhaust pipe 65 branches into two. One is connected to vacuum pump 70 via valve 68, and another is connected to container 71 via valve 69.
In the manufacturing equipment as configured above, the pressure inside PDP 60 is first reduced by opening valve 68 of vacuum pump 70 while heating PDP 60 with heater 66 so that impurity gases are exhausted from inside the PDP. Then, valve 68 is closed and valve 69 is opened to inject discharge gas containing neon and xenon from container 71. Lastly, the exhaust pipe 65 is heated and fused at near the PDP to seal and complete the PDP in which discharge gas is sealed inside.
In addition to exhausting impurity gases from inside PDP 60, the Japanese Laid-open Application No. 2000-311588 discloses the adsorption of impurity gases by providing a getter inside PDP 60. The Japanese laid-open Patent No. H11-329246 also discloses a method of adsorbing impurity gases by providing a getter inside exhaust pipe 65.
However, in the above conventional methods, discharge gas is injected through the exhaust pipe. Since impurity gases exhausted from the PDP are adsorbed onto the inner wall of the exhaust pipe, impurity gases re-enter the PDP together with the discharge gas when feeding in the discharge gas, resulting in their insufficient removal. With the method of adsorbing impurity gases by providing a getter inside the PDP, the getter's effect does not extend over the entire area, since the discharge space is divided by the partitions. Partially remaining impurity gases causes uneven display. Furthermore, the getter, when heated by electric discharge during use, allows impurity gases to be released into the PDP again. With the method of removing impurity gases by providing a getter inside the exhaust pipe, impurity constituents are gradually accumulated on the getter, and thus its capability to remove impurity gases declines over a period.
The present invention aims to solve the above disadvantage, and offers a highly reliable PDP with improved display characteristic and less degraded phosphor by reliably keeping inside the PDP clean so as to suppress erroneous discharge and reduced luminance.